The barrier effect of polymeric materials and films with respect to water vapor is generally independent of the barrier effect with respect to oxygen. Accordingly, materials exhibiting a good vapor barrier will not necessarily also exhibit a good barrier with respect to oxygen and to odors, and vice versa. The only material that exhibits a barrier effect in a moderate to good range of values not only with respect to oxygen but also with respect to water vapor is polyvinylidene chloride (PVDC). PCTFE, polyolefins, and other polymers exhibit a good to very good water vapor barrier but a very low oxygen barrier. EVOH (ethylene-vinyl alcohol copolymer) exhibits a very good oxygen barrier, but a low water vapor barrier. There is currently no available polymeric packaging film that is marketable, i.e. that can be produced cost-effectively, and that exhibits a high water vapor barrier alongside a high oxygen barrier. On the other hand, modern medicaments are increasingly proving to be sensitive to water vapor and oxygen. The requirements placed upon the barrier effect exhibited by packaging films for medicaments are accordingly ever more stringent. The requirement hitherto has been for a large barrier effect mainly with respect to water vapor, but packaging films for modern medicaments now also have to exhibit a large barrier effect with respect to oxygen.
Thermoformable plastics films are widely used for the packaging of food and drink, medicaments, and other products. The products known as blister packs are important here. Blister packs have a shape matched to the product and obtained by thermoforming of a flat, preferably transparent plastics film. The packaging component that conforms to the respective product or contents is also termed base component, and after the contents have been charged it is sealed with a lid film, preferably an aluminum film, by a welding or sealing process. The packaging has to comply with particular requirements in respect of the barrier effect thereof with respect to water vapor, oxygen and sometimes other gases, such as carbon dioxide, and these requirements depend on the intended application. By way of example, a wide variety of medicaments require packaging exhibiting a water vapor transmission of less than 0.06 g/(m2·24 h), and in some cases less than 0.04 g/(m2·24 h). In the case of transparent films, the only way of achieving water vapor transmission of less than 0.06 g/(m2·24 h) is to use PCTFE as film material with a thickness greater than 100 μm. Water vapor transmission below 0.04 g/(m2·24 h) has hitherto been achievable only by using aluminum film, in particular by using what is known as “cold form film”. Aluminum films of this type are not transparent and they moreover have low deformability, and cannot therefore be used to produce relatively small blisters, so that the film area needed is substantially greater than when a thermoformable blister is used.
Thermoformable plastics films have to have not only a larger barrier effect but also other properties, such as sealability, freedom from streaks, low thickness, uniform thickness profile, and good processability. For the processability, especially advantageous features are good deformability, i.e. maximum uniformity of thickness distribution in the component after the deforming process, and also maximum shape replication, minimum curl, and a small coefficient of friction, i.e. good slip capability with respect to the machinery parts contacted and the packaged contents. The curl occurs in two- or multilayer composite films when the coefficients of thermal expansion (CTEs) of the individual layer materials differ.
Thermoforming plastics films for packaging exhibiting barrier effect with respect to water vapor are known in the prior art.
EP 1 655 237 A1 discloses a thermoformed or cold-formed blister pack with a blister base component and with a lid film. The lid film is composed of an aluminum film of thickness from 10 to 30 μm which has been laminated or coated with, on a first side, a film which can be peeled from the aluminum film and which is made of at least one plastics layer based on thermoplastic or thermoset polymers and, on the second side, sealed against the blister base component, a plastics film based on polyvinyl chloride (PVC) having a film thickness of from 10 to 40 μm, or polyvinylidene chloride (PVDC) having a film thickness of from 10 to 40 μm, or polypropylene (PP) having a film thickness of from 6 to 35 μm, or polyethylene (PE) having a film thickness of from 6 to 35 μm, or polyester having a film thickness of from 5 to 10 μm, or polychlorotrifluoroethylene (PCTFE) having a film thickness of from 8 to 30 μm, or cycloolefin copolymers (COCs), or cycloolefin polymers (COPs) having a thickness of from 10 to 40 μm. The blister base component is composed, at least on the side sealed against the lid film, of a material having a chemical structure compatible with that of the plastics films sealed against the blister base component. The film that can be peeled from the aluminum film is composed of one or more layers made of one or more of the following plastics: PVC, PVDC, PCTFE, PP, PE, polyester, polyethylene naphthalate (PEN), polyamide (PA), COC, COP, polystyrene (PS), or cellophane.
EP 1 468 817 A1 (whose United States equivalent is United States Publication No. 2007/068842A1 relates to a lid film for blister packs with thermoformed or cold-formed blister base components. The lid film encompasses an aluminum film of thickness from 5 to 30 μm which has been laminated, on a side provided for sealing with respect to a blister base component, with a plastics film based on PVC having a film thickness of from 10 to 40 μm, or PVDC having a film thickness of from 10 to 40 μm, or PP having a film thickness of from 6 to 35 μm, or polyester having a film thickness of from 5 to 15 μm, or PCTFE having a film thickness of from 8 to 76 μm, or COC having a thickness of from 10 to 40 μm. Blister base components are composed by way of example of films made of PVC, PP, PET, PE, and of composite films, such as PVC/ACLAR® (PCTFE), PVC/PVDC, and COC, or Al—Al blisters.
DE 602 09 812 T2 (whose United States equivalent is United States Publication No. 2003/099813A1 describes an at least single-layer polymer film, where one of the layers encompasses a vinylidene chloride composition which encompasses 100 parts by weight of vinylidene chloride copolymer; from 0.1 to 10 parts by weight of stabilizer, from 0.1 to 10 parts by weight of lubricant, and from 0.1 to 10 parts by weight of hydrophilic clay. By way of example, the structure of the polymer film is of the following type: C/A/B, B/A/D/B, or C/A/D/C, where A stands for PVDC.
The packaging films known in the prior art exhibit inadequate barrier effect with respect to water vapor and oxygen, or require the use of considerable amounts of PCTFE, of an aluminum film, or of inorganic additives. These measures are associated with increased costs in the case of PCTFE, or impair processability and other properties, such as optical transparency.
PCTFE film exhibits a very good water vapor barrier, but a low oxygen barrier. An increase in the thickness of a PCTFE film can in principle raise the water vapor barrier, but because of indirect proportionality between material thickness and water vapor transmission the thickness of PCTFE needed rises rapidly into a range which is technically and economically very disadvantageous, and there is no possibility of achieving an oxygen barrier adequate for highly demanding packaging applications. PVDC, on the other hand, exhibits a very good oxygen barrier, but exhibits a water vapor barrier substantially smaller than that of PCTFE. If the same water vapor barrier is to be achieved with PVDC as with PCTFE, the thickness of PVDC has to be 165% of the thickness of PCTFE. PVDC films and, respectively, layers are usually produced by applying many thin sublayers. By way of example, the weight per unit area of PVDC required to achieve a water vapor barrier of 0.035 g/(m2·24 h) (measured at a temperature of 38° C. and a relative humidity of 90%) would be about 400 g/m2. This requires 40 passes through the machinery of a conventional industrial coating system in each case applying 10 g/m2, or 27 passes at 15 g/m2. Such a large number of passes through machinery is not achievable either technically or economically. The industrial processes known in the prior art produce PVDC layers with weight per unit area of up to at most 180 g/m2.
The oxygen barrier exhibited by PVDC is only very slightly affected by moisture, whereas by way of example EVOH, which likewise exhibits a very good oxygen barrier, suffers major loss of oxygen barrier on exposure to moisture. In extreme cases, the magnitude of the loss in the case of EVOH extends to powers of ten. EVOH is usually used in packaging for food or drink, but has also recently been used in pharmaceutical packaging.